Methods, systems and/or arrangements, falling within the above technical field and the above mentioned natures, are previously known in a plurality of different forms and/or embodiments.
By way of introduction, it may be mentioned that it is previously known different arrangement adapted to relate to and to form a part of a subsea electric power distributing AC-system, and adapted for a deep subsea application, said arrangement thus being enclosed in a watertight, and normally with an oil filled, casing.
Said casing is exposing a main power input connection, adapted for a watertight co-ordination with usually a very long first subsea cable, supplying the required AC-voltage and AC-current.
The length of such first subsea cables may be, for some applications, in the range of up to 200 km and above and the power supply may be up to 200 MVA and above, which means that special criteria and application must be considered when connecting and/or disconnecting such a high load consumer, such as a device or an equipment, usually in the form of an electric AC-three phase motor or the like.
It is here to be mentioned that an AC-voltage drop, caused by the area of the used conductors and the actual length of the 3-phase power feeding cable at a specific load, is high and that the AC-voltage, during a NO-load condition, is to be chosen much higher than the normally required AC-voltage, adapted to the actual consumer.
This means that a used 3-phase AC-motor normally is to be dimensioned for a high and predetermined start up AC-voltage and an expected high start up AC-current, by and when applying a direct starting mode.
For this application it is to be used means for an “ON-load switching means”.
It is further to realize that in such an application it is essential to choose a large conductive area for the used subsea cable, for compensating for any mentioned AC-voltage drop, at least during the initial starting up mode.
A main power output connection, related to said casing, is adapted for a similar watertight co-ordination with a second subsea cable, said second subsea cable being adapted for a power supply to an AC-current and AC-voltage adapted consumer, such as a device or an equipment, as illustrated above.
Within such an arrangement it is normally enclosed an AC-voltage transformer means, adapted to a fixed AC-voltage transforming ratio, to compensate for any AC-voltage drop, caused by a cable related resistance, inductance and/or capacitance.
As the electrical criteria, related to the consumer's device or equipment in the form of an AC-load, is calculated and known as to its starting mode and its effect as well as the length of and other criteria related to the mentioned first subsea cable supplying the required AC-voltage, the construction of the used arrangement, based upon the length of and the other criteria related to the mentioned second subsea cable, connected to the consumer's device or equipment, as the AC-load, the AC-voltage transformer means may be set to a calculated value or ratio.
Within said casing and related to said arrangement may also be enclosed an AC-load circuit disconnecting (breaking) or connecting means, adapted for a direct disconnecting or breaking of an AC-loaded connection or adapted for a direct connecting of an AC-loaded connection, however such breaking or connecting means are complicated in construction, in order to withstand any caused arc development, when breaking and connecting large effects, especially capacitance or reactance related or exposing circuits.
It is however in this application also previously known to use a so called NO-load disconnecting or breaking and connecting means, which is adapted to activate a breaking mode or a connecting mode at a regulated AC-voltage at 0-level and thereafter, by frequency control means connect the load to an increasing AC-voltage.
The present invention has its use in a NO-load disconnecting or breaking mode and a connecting mode and used within a subsea application.